In certain industries it is necessary to remove as much of an original environment from contact with a product as possible and to replace it with a new environment. Fat and oil containing foods, for example, are very susceptible to attack from oxygen and can be preserved much longer in its absence. A near complete removal of oxygen from containers for storing oxygen-sensitive products has, until now, required complex and/or expensive equipment and often has required specialized and/or expensive containers.
Oxygen removal has traditionally been accomplished by packaging under vacuum. Vacuum pressure can be described in terms of inches of mercury, with zero inches being normal atmospheric pressure and approximately 30 inches being a perfect vacuum. The percentage of original oxygen remaining after applying a vacuum to a container is inversely proportional to the level of vacuum applied, for a single stage vacuum system. For example, a container originally exposed to a normal atmosphere would retain only about 17% of its original oxygen content after application of a 25 inch vacuum. This is calculated according to the equation: ##EQU1## In other words, about 83% of the original oxygen would be removed using a single stage vacuum packaging operation which applies 25 inches of vacuum.
If one were to repeat the above operation by refilling the container with an inert gas and then applying a second stage of 25-inch vacuum, the percentage of original oxygen theoretically remaining in the container would be: EQU =17%.times.(1-25 inches/30 inches )=2.8%
In actual practice, however, it has been found that the oxygen content is not significantly further reduced, even when the operation is repeated as many as four or five times. The suspected reason for this is that when vacuum is drawn on a container with a single open end and the container is then filled with inert gas from the same open end, the oxygen remaining as part of the original atmosphere will initially concentrate at the bottom of the container while the inert gas will fill the top. If vacuum is again applied before the remaining oxygen has mixed with the inert gas, the gas removed by the vacuum will consist primarily of the inert gas just added and will contain very little of the remaining oxygen.
Therefore, in order to achieve a near complete removal of oxygen using prior art systems it has been necessary to draw a very high degree of vacuum in the container. This requires very expensive and complex equipment. Furthermore, in order to package oxygen-sensitive products under vacuum, it is necessary to utilize relatively sturdy (and expensive) container materials which ar capable of withstanding such vacuum for extended periods of time.
One technique for supplying a controlled environment utilizes individual "bell jar" enclosures which surround the container. Such a device is disclosed, for example, by U.S. Pat. No. 2,292,887 issued to McBean. Although such devices may be adapted for continuous operation, the apparatus necessary for moving the container and/or the "bell jar" relative to one another adds considerable complexity and cost to the device. Robinson U.S. Pat. No. 3,508,373 discloses a reservoir to which vacuum and gas are alternately applied to remove the oxygen from a package positioned therein.
Other devices are known which cooperate directly with the opening of the container to apply, for example, a vacuum or inert gas substantially to the interior of the container only. U.S. Pat. No. 2,457,690 issued to Kronquest discloses an example of such a vacuum-head apparatus. Such devices, however, are complex, and are not readily adaptable to use with containers having differing configurations and sizes. Furthermore, if the product is packaged under vacuum, the container must be sufficiently durable to withstand the pressure of the atmosphere both before and after sealing.
It is further known to utilize a multichambered rotary drum, in which individual chambers may accept a container to be subjected to the controlled environment. As the drum rotates, the chambers transporting the containers move past and engage an outer enclosure which seals the opening of the chamber, and a vacuum or other environment is applied. U.S. Pat. Nos. 1,751,643 issued to Malmquist, 2,521,746 issued to Preis, and 1,774,529 issued to Sharp illustrate various configurations of such known devices.
A particularly advantageous rotary drum device overcoming many of the foregoing problems associated with the prior art devices by replacing a rigid outer enclosure with a substantially continuous flexible belt enclosure. Such a device is disclosed in application U.S. Ser. No. 818,386, now U.S. Pat. No. 4,658,566, the entire disclosure of which is incorporated herein by reference.
In order to overcome the shortcomings of the prior art, it is an object of the current invention to obtain nearly complete exchange of environments in containers. Another object is to provide the containers with such a controlled environment without necessarily utilizing very high vacuum.
A further object of the invention is to provide a method for imparting a controlled environment to one or more containers at or near atmospheric pressure prior to sealing, allowing the use of less expensive container materials than used for the vacuum-packaging devices of the prior art. A related object is to provide an apparatus which achieves the desired near-total atmospheric exchange or control without at any time subjecting the container walls to significant pressure differentials.
One specific object is to provide a rotating drum method which accomplishes near complete removal of a first environment (such as oxygen-containing air) from a sequence of containers and which replaces such first environment with a second environment (such as a substantially inert gas).
A further object is to provide a rotary drum method for providing a controlled environment to one or more containers which provides a secure closure of desired individual chambers during rotation of the drum without significantly interfering with such rotation. A related object is to provide such a method which does not introduce significant friction between the sealing enclosure and the rotating drum.
An important object of the present invention is to provide such a method for use in a continuous processing operation, which is simple and which is therefore economical and highly reliable.
Another object is to provide such a method which can be used to provide a controlled environment to varying sizes and configurations of jars and other containers, including containers of different heights. A further related object is to provide such a method which can be used with containers of differing diameters.
These and other objects shall be apparent in light of the present specification.